The abiotic environment is dependant largely on ecological succession. The first way ecological succession shapes the abiotic environment is through edaphic factors. A sand dune for example begins with an inhospitable salty soil which contains very few mineral ions. However as these plants die their organic matter is left in situ. This decomposes and the organic matter contributes to the soil, this would include minerals such as nitrates and phosphates. This alters the pH making it less alkaline and the number of mineral ions steadily increases. Through the different stages of succession the soil becomes more hospitable allowing for larger plants which would then eventually decompose and keep contributing towards the edaphic factors allowing for larger plants to go. With more and more plants being able to survive in an area (due to an increase in the carrying capacity of the area) this means that water availability would decrease. Each plant sets roots into the soil which draw up water from the soil. At the start of succession, with the pioneer species, there may be a large amount of water available however when the climax community (consisting mainly of trees) is present they draw up a large volume of water leaving far less in the water. These roots, along with contributing to water availability, also make the soil more compact as the roots get into the soil and it becomes much more firm as soil and roots become intertwined. This means it is harder for future species to grow as it may be harder for future species to grow their roots to a sufficient length. The roots may also stop water run off which in heavy rain could cause flooding as the roots block and jam the water as it tries to run off. Light levels / availability for plants also changes throughout ecological succession. In the initial stage of succession there are very few pioneer species and the plants themselves are small. This means there is very little competition (either inter or intraspecific) between the plants. They can all get sufficient nutrients and light. However in stages similar to the climax community a taller plant may block the light from reaching small plant which does not grow upwards. The most obvious example being a large oak tree in the climax community shielding light from reaching a bush by the base of the tree.
I think I got 5 out of 6 for this answer. I shoul have expanded on my point about the root systems and should have mentioned their affect on soil erosion. I could have also discussed nitrogen fixing bacteria and their role in succession
Mark Scheme
I think I got 5 out of 6 for this answer. I shoul have expanded on my point about the root systems and should have mentioned their affect on soil erosion. I could have also discussed nitrogen fixing bacteria and their role in succession
Mark Scheme
- nitrogen-fixing bacteria in pioneer
- plants / lichen can introduce nitrate to soil;
- taller plants provide shelter from lower temperatures / frost;
- humus resulting from pioneer plants /
- lichens adds organic matter to soil;
- increased soil structure enables soil to retain moisture;
- enabling new species to grow;
- new species contribute more nitrogen to soil;
- leaves and fallen trees can acidify alkaline soils;
- low acid and higher nitrate levels in soil allow
- another species (spruce) to grow;
- larger trees with deeper root systems can reduce soil erosion;
- acid secretion of lichens help break down rock;
- presence of plants lead to greater recycling of nutrients
- (fundamental in phosphorous cycle);